Apparatus for layerwise producing an object using laser sintering

ABSTRACT

An apparatus for layerwise production of an object using laser sintering by solidifying a material which is solidifiable by electromagnetic radiation comprises a device (5) for producing an electromagnetic beam (6) and a focusing device (8) for focusing the beam (6) onto the material within a working plane (7), whereby the focusing device (8) comprises a lens (9) and a mount (10) holding the lens (9), a ring nozzle (12) arranged adjacent to the image-side surface (11) of the lens (9) facing the working plane (7), the ring nozzle having its outlet oriented relative to the image-side surface (11) so that a discharged stream strokes tangentially along the image-side surface (11) towards the center, the inlet of the ring nozzle being selectively connected with a source of pressurized gas.

The present invention relates to an apparatus for layerwise producing anobject using laser sintering.

The applicant is aware of an apparatus for layerwise producing an objectusing laser sintering, the apparatus comprising a support forpositioning the object in relation to a working plane and a device forapplying a powder which can be solidified by electromagnetic radiation.The apparatus further comprises a laser. The laser beam produced by thelaser is focused onto a point within the working plane by means of afocusing device comprising a lens and solidifies the powder. Especiallyin case that polyamide is used as the powder material, monomers escapefrom the powder and precipitate on the lens, whereby the transparencythereof is progressively reduced in the course of the building process.This causes a progressive absorption of the laser beam, whereby itsintensity at the working plane decreases. Owing to the decreasingintensity the quality of the object to be formed is reduced. In order toovercome this problem a protecting glass is arranged in front of thelens and nitrogen is blown out of a plurality of nozzles onto theprotecting glass. However, since the nitrogen flows over part of theprotecting glass only and no flow exists between the nozzles, themonomers precipitate at these places. Thus, the protecting glass must beremoved and cleaned after each building process of an object.

It is the object of the invention to provide an apparatus for layerwiseproducing an object by laser sintering wherein the focusing unit iseffectively protected against contamination.

This object is achieved by the apparatus comprising a device forproducing an electromagnetic beam and a focusing device for focusing thebeam onto the material within a working plane, whereby the focusingdevice comprises a lens and a mount supporting the lens, a ring nozzlearranged adjacent to the image-side surface of the lens facing theworking plane, the ring nozzle having an outlet directed in relation tothe image-side surface so that an outflowing stream strokes tangentiallyalong the image-side surface towards the center, the inlet of the nozzlebeing selectively connected to a source of pressurized gas.

The apparatus is advantageous in that the nitrogen blown through thering nozzle flows over the entire lens surface facing the working plane.Since the nitrogen is blown in a tangential direction of the lenssurface, the flow produced is directed from the outer side of the lenstowards the center thereof and therefrom towards the working plane. Thisflow efficiently prevents the precipitation of monomers on the lenssurface. Hence, cleaning of the lens is required at considerably longerintervals.

Further features and advantages of the invention will be apparent fromthe description of embodiment with reference to the Figures. In theFIGS.

FIG. 1 is a schematic block diagram of the apparatus; and

FIG. 2 shows a section through the ring nozzle.

As shown in FIG. 1 the apparatus for layerwise production of an objectcomprises a support 2 which supports the object to be formed and whichis movable in vertical direction within a tank 1 having an open top. Thesupport 2 is vertically adjusted so that the respective layer of theobject to be solidified is in a working plane 7. Moreover, a coatingdevice 3 is provided for applying the powderous building material whichcan be solidified by electromagnetic radiation. The apparatus comprisesa laser 5. The laser beam 6 produced by the laser 5 is focused onto apredetermined point within the working plane 7 by means of a focusingdevice 8.

As shown in FIG. 2, the focusing device 8 comprises a lens 9 and a mount10 supporting the lens 9. The lens 9 comprises an image-side surface 11facing the working plane 7. A ring nozzle 12 having an inlet connection13 is provided in the mount 10. A reservoir containing a pressurized gasis coupled to the inlet connection 13 through a valve. Preferably,nitrogen is used for the gas. The ring nozzle 12 is arranged in themount 10 adjacent to the image-side surface 11. The nozzle outletorifice 14 is directed towards the image-side surface 11 so that thedischarged gas stream flows tangentially across the image-side surface.

In operation the valve is opened and nitrogen flows through the inletconnection 13 into the ring nozzle 12 and out through the nozzle outletorifice 14. The outflowing gas strokes across the entire image-sidesurface 11 of the lens 9 in a direction tangentially thereto. The gasflows radially towards the center of the lens 9 and therefrom indirection towards the working plane 7 so that monomers produced whensolidifying the powder can not precipitate on the lens 9.

We claim:
 1. Apparatus for the layerwise production of an object bylaser sintering a material which can be solidified using electromagneticradiation, the apparatus comprising:means for producing a layer of saidmaterial extending along a working plane, means for generating a beam ofelectromagnetic radiation, focusing means for focusing said beam ontosaid layer of said material, said focusing means comprising:a lenssystem having an image-side surface facing said working plane, mountingmeans holding said lens system, a ring nozzle arranged adjacent to saidimage-side surface of said lens system, said ring nozzle having an inletand a nozzle outlet orifice, a source of a pressurized gas; and meansfor selectively connecting said nozzle inlet to said source ofpressurized gas, said nozzle outlet orifice being oriented relative tosaid image-side surface for directing a flow of said pressurized gastangentially across the entire image-side surface from its peripheryradially towards its center.
 2. The apparatus of claim 1, wherein saidpressurized gas source is nitrogen source.
 3. The apparatus of claim 1,said focusing means further comprising a passage between said inlet andsaid ring nozzle, said passage having a reduction in size causing a bendin the direction of flow of pressurized gas.